What is the meaning of the LED on the SFP and the Ethernet side?

On the side of the SFP are three LED:

SFP ACT: SFP Activity ( data is transmitted).

SFP LINK: Fiber is attached.

Some yellobriks have ethernet RJ-45 Sockets:

ETH Link (green) | ETH Activity (yellow) || ETH Link (green) | ETH Activity (yellow)

This is valid for the devices Oxx15x0 (e.g. OET1510).